1. Field of the Invention
The invention pertains to electrically controlled devices for switching optical signals and more particularly to electrically controlled devices for coupling arbitrarily polarized optical signals between predetermined pairs of terninals.
2. Description of the Prior Art
High information transmission capacity, immunity to electro-magnetic interference, and freedom from grounding problems ideally suit optical transmission systems for linking distributed computers and computer controlled industrial system components. Since these optical transmission systems often utilize optical fibers to serially link a multiplicity of electrically driven optical repeater stations, a power failure at one of the stations interrupts the data chain and causes the entire system to fail. To prevent such a catastrophe, a fail safe optical switch is employed at each repeater and component station to optically bypass the station that loses local power. These fail safe switches must possess low insertion loss properties, provide high isolation between the input and the output fibers during the "Power On" mode, and must function effectively with unpolarized light coupled thereto from a multimode fiber. Electro-optic switches, as for example, 2.times.2 cross bar switches, of the prior art possess sufficiently low insertion loss, but do not provide the desired optical isolation between the input and output terminals during the energized switch mode. Tandem arrangements of these switches, as described in U.S. Pat. No. 4,011,543, issued to Soref, et al. on Mar. 8, 1977 and assigned to the assignee of the present invention, may provide the desired performance but appreciably increase the number of components employed and concomitantly the cost of the switches.